The present invention relates to the field of froth flotation used in the separation process, and more particularly, embodiments of the invention relate to the process and apparatus for enabling flotation of particles via their attachment to carrier bubbles.
Industrial processes that employ air bubbles flotation for particle separation are widely available. They aim to efficiently recover particles such as minerals, coal, oil sands and paper in mining and recycling industries. The current deficiency that hampers efficient and economic recovery of large particles is the weak attachment between carrier bubbles and particles. The state of the art in the mining industry currently allows the flotation of particles with an upper size limit of about 100 micrometer for minerals and 600 micrometer for coal. To reach smaller sizes then these values, fine grinding of the ore is required which leads to undesirable particle contamination, dust tailing and large economical expenses.
Froth flotation uses the ability of bubbles to preferentially attach to hydrophobic surfaces. This allows the selective separation of hydrophobic and hydrophilic particles. For instance in the mining industry, the ores are ground to liberate the valuable minerals. The ground rock including the liberated minerals is then mixed with water to form a slurry. Chemicals are added to the slurry which selectively bind to target minerals to enhance their hydrophobicity and thus their separation through froth flotation.
Diverse methods have been proposed to generate bubbles. Instances of these include: bubble generation using ultrasound techniques, shaking and stirring method (hydrodynamic cavitation) in which the liquid is stirred and the gas is sheared to generate bubbles, the use of chemical reactions to generate gas in a liquid, the control of pressure namely its increase to dissolve the gas in solution and its reduction to create bubbles from supersaturated dissolved gas, the use of waves with frequencies less than 1 kHz that are applied to a porous material through which gas is injected in a liquid, and other methods that include high frequency waves, such as microwaves, to locally increase the liquid temperature to generate bubbles. All these methods with the exception of the microwave method, generate bubbles with a large volume distribution.
The efforts involving the recovery of large particles have been addressed by using bubbles with an oily coating and increasing the hydrophobicity of particles. These methods rely on enhancing the attachment of the oily coating of the bubble to the particle and facilitating the expansion of the triple point contact line. The latter leads to an increase of surface contact area between the bubble and the mineral particle, facilitating the attachment.